An information reproducing system for reproducing the video information recorded on, for example, a video disc usually has a time-axis error signal generator incorporated therein. The time-axis error signal generator detects the time-axis variation in the video signal to be reproduced and produces a time-axis error signal to make a time-axis correction of the video signal. A known variant of such a time-axis error signal generator is constructed in such a manner as to produce a timing signal through detection of a specific point of a color burst signal and to compare the phase of the timing signal with the phase of a reference horizontal synchronizing pulse extracted from a reference signal generator. The time-axis error signal generator produces as the time-axis error signal a signal representative of the difference between the respective phases of the two signals thus compared with each other. The specific point of the color synchronizing burst is usually given as a point at which the burst crosses a preselected reference level. A time-axis error signal generator of the above described nature is however not fully acceptable since correct and reliable time-axis error signals can not be produced during vertical synchronizing pulse intervals when color synchronizing bursts are absent in the composite video signal.
Another prior-art variant of a time-axis error signal generator is constructed so that a time-axis error signal is produced upon comparison of the phases of the played back horizontal synchronizing pulses in the video signal with a phase of a reference horizontal synchronizing signal. From a theoretical point of view, the time-axis error signal produced by such a time-axis error signal generator must be fully dependable since the horizontal synchronizing pulses are present during vertical synchronizing pulse intervals.
As well known in the art, synchronizing signal components of a composite video signal are separated from the composite video signal by clamping the pedestal or synch-tip level of the composite video signal to a predetermined voltage level and thereafter slicing the signal at a desired level to produce synchronizing pulses. The accuracy of clamping as achieved in the separation of the synchronizing pulses in this fashion depends primarily on the signal-to-noise ratio in the supplied composite video signal and the stability of the clamping circuit against noise. The clamped level of the composite video signal is thus subject to fluctuation and, for this reason, the synchronizing signals separated from the composite video signal tend to vary in phase when the fall-times of the synchronizing pulses contained in the composite video signal and the clamped level of the composite video signal vary. This means that a satisfactorily high accuracy can not be achieved when a time-axis correction is made with use of a time-axis error signal produced through detection of the time-axis fluctuations of the video signal on the basis of the horizontal synchronizing pulses obtained from the synchronizing signals separated from a composite video signal as in the latter type of time-axis error signal generator.
It is, accordingly, a prime object of the present invention to provide a synchronizing signal separator network in which a time-axis correction of the composite video signal can be effected with satisfactory accuracy by producing a synchronizing signal with supressed phase variation.